According to a new report by a group of Stanford University graduate students, the shortfall facing California’s public pension systems could reach more than half a trillion dollars over the next decade and a half.

A summary of the report, released Monday, also said the current recession has cost the three systems — for the state’s public employees, schoolteachers and University of California workers — $109.7 billion in lost investment value. The report says the systems’ basic growth assumptions are too rosy.

The report was prepared for Gov. Arnold Schwarzenegger, who has made pension reform a top issue his last year in office. Because pension benefits are guaranteed, the state’s general fund, facing a $19 billion deficit through next summer, must make up any shortfalls.

“This study reinforces the immediate need to address our staggering pension debt,” the governor said in a statement. “The consequences are clear: increasingly large portions of state funding for programs Californians hold dear such as schools, parks and health care will be diverted to pay for this debt.”

The report’s proposed changes echo the governor’s, many of which are politically difficult: reducing benefits for new employees, raising annual contributions to ward off shortfalls and shifting workers to a partial 401k system. High pension costs also are a growing concern for California’s cities and counties, as well as for other states.

Otto Warmbier was arrested in January 2016 at the end of a brief tourist visit to North Korea. He had been medically evacuated and was being treated at the University of Cincinnati Medical Center when he died at age 22.